fix: self-registered users don't get execute perms

http/auth.go

@@ -171,6 +171,12 @@ var signupHandler = func(_ http.ResponseWriter, r *http.Request, d *data) (int,
 	// if that is the default permission.
 	user.Perm.Admin = false
 
+	// Self-registered users should not inherit execution capabilities from
+	// default settings, regardless of what the administrator has configured
+	// as the default. Execution rights must be explicitly granted by an admin.
+	user.Perm.Execute = false
+	user.Commands = []string{}
+
 	pwd, err := users.ValidateAndHashPwd(info.Password, d.settings.MinimumPasswordLength)
 	if err != nil {
 		return http.StatusBadRequest, err